Elderly listeners often experience poorer speech intelligibility than younger listeners, particularly in the presence of noise. Although an age- related reduction in hearing sensitivity likely contributes to this finding, recent scientific research suggests that an age-induced deficit in suprathreshold auditory processing may be present even in the absence of clinically significant hearing loss. Specifically, aging may result in a reduction in the cochlear nonlinearity which in turn may adversely affect suprathreshold processing. The cochlear nonlinearity, which is thought to reflect the functioning of the outer hair cells in the cochlea, is responsible for high sensitivity, sharp frequency tuning, and enhanced spectral contrasts via suppression. Thus, any reduction in the magnitude of the nonlinearity may result in one or more functional deficits, possibly including impaired speech intelligibility. The long-term goal of the proposed research is to further our understanding of the auditory processing of elderly listeners. In particular, this project will evaluate multiple psychophysical estimates of cochlear nonlinearity in young and aged listeners both with normal hearing and with mild- to-moderate hearing loss. For all proposed experiments, two different signal frequencies will be examined, one relatively low and one relatively high; these frequency regions may normally differ in their strength of nonlinear processing and thus differences between young and elderly listeners may be greater at the higher frequency. Thus, the purpose of this study is to examine multiple measures of cochlear nonlinearity in the same group of subjects to determine whether or not an age-related decline in the nonlinearity exists. The ultimate goal is to provide a better understanding of the listening difficulties experienced by elderly listeners.